Electron beam tubes and circuits therefor



Nov. 10, 1959 J. s. DONAL, JR, ET 2,912,613

ELECTRON BEAM TUBES AND CIRCUITS THEREFOR Filed July 14. 1953 3Sheets-Sheet 1 Nov. 10, 1959 J. s. DONAL, JR., ETAL 2,912,613

ELECTRON BEAM TUBES AND CIRCUITS THEREFOR Filed July 14. 1953 3Sheets-Sheet 2 United States ELECTRON BEAM TUBES AND CIRCUITS THEREFORApplication July 14, 1953, Serial No. 367,850

11 Claims. (Cl. 315-516) The present invention relates to' electron beamtubes and circuits therefor, and particularly to beam tubes of theelectron coupler type used as phase discriminators, amplitude modulatorsor balanced modulators.

In an electron coupler tube, as described in C. L. Cuccia Patent No.2,452,797, assigned to Radio Corporation of America, an electron beam isprojected along a path extending in succession through an input regionupon which is impressed a radio frequency electric field transverse tothe beam path and an output region to which the beam gives up energy byinducing a second transverse radio frequency field. Each of the tworegions includes a pair of opposed field-defining electrodes located onopposite sides of the beam path and coupled to a resonant circuit, whichmay be either an external circuit or some form of cavity resonatorforming part of the tube structure itself. The input and output circuitsare adapted to be coupled to a radio frequency source and a useful load,respectively. The beam is subjected to a constant axial magnetic field.The magnetic field strength H is adjusted to a value such that theangular cyclotron frequency of an electron in said field is equal towhere e and m are the charge and mass, respectively, of an electron, andw is the angular frequency of the radio frequency field set up in theinput region. Under these conditions, as the beam passes through theinput region the electrons are caused by the crossed electric andmagnetic fields to move in spiral paths of increasing radii about theatent Another object is to provide an improved amplitude modulator tube.

Still another object is to provide a tube which will serve as a balancedmodulator.

These and other objects are achieved in accordance with the invention byincorporating the basic principles of the Cuccia electron coupler in anelectron coupler tube having three separate radio frequency electricfield regions, two of which are input regions and the other of which isan output region, with two coupling beams. Two embodiments of the tubeare illustrated, in the first of which the three regions are provided bythree coaxial resonators arranged in a row with an electron gun locatedadjacent to each end resonator and a coloriginal beam axis, absorbingenergy from the input region and the radio frequency source coupledthereto. Since they have the same angular and axial velocities, all thespirally traveling electrons in the beam lie at any instant on thelinear directrix of a cone, and the envelope of the rotating orrevolving beam is a cone. Hence, the beam is sometimes termed acone-directrix or rotating pencil beam. In the output region therotating beam gives up spiral energy to the region and coupled load byinducing radio frequency voltages on the field defining plates andthereby setting up a transverse radio frequency field in that region. Asspiral energy is abstracted from the beam the radii of the electronpaths are progressively reduced, and hence, the envelope of the beam inthe output region is an inverted cone. The electron coupler tube may beused as a modulator by coupling an unmodulated carrier signal to theinput region and modulating the beam current or the transit time by amodulating signal thus producing a modulated carrier signal in theoutput load, as disclosed in said Cuccia patent. On the other hand, anamplitude modulated signal coupled to the input region will befaithfully reproduced in the output of the device.

The principal object of the present invention is to provide a singleelectron tube which will perform all of the functions of aphase-discriminator circuit.

lector located between each pair of adjacentresonators in such mannerthat each beam passes through an end resonator and the middle resonatoronly. Two input sources are coupled respectively to the end resonators,and the middle resonator is coupled to a useful load. In the other tubeembodiment illustrated, the two input resonators and associated electronguns are arranged side-by-side and the output resonator surrounds theextensions of the two beam paths beyond the input resonators. Schematiccircuits are also included to illustrate the uses of the tube as a phasediscriminator, an amplitude modulator and a balanced modulator.

In the accompanying drawings:

Fig. l is a longitudinal sectional view, partly schematic, of oneembodiment of a phase discriminator electron coupler tube incorporatingthe invention;

Figs. 2 and 3 are transverse sectional views taken on lines 22 and 3-3,respectively, of Fig. 1;

Fig. 4 is a view similar to Fig. 1 of another embodiment of a phasediscriminator tube incorporating the invention;

Fig. 5 is a transverse sectional view taken on line 55 of Fig. 4;

Fig. 6 is a vector diagram showing the combination of radio-frequencyvoltages in the operation of an embodiment of the invention;

Fig. 7 is a longitudinal sectional view, partly schematic, showing aparticular utilization of a phase discriminator tube incorporating theinvention;

Fig. 8 is a transverse sectional view, partly schematic, showing anotherparticular utilization of a phase discriminator tube incorporating theinvention; and

Fig. 9 is a schematic transverse sectional view showing still anotherparticular utilization of a phase discriminator tube incorporating theinvention.

Referring first to Figs. 13, there is shown an electron tube having anelongated metal envelope ll. Within the envelope, and spaced as shown inFig. 1 on opposite sides of the longitudinal central axis ZZ of thetube, are mounted by suitable means two electron guns consisting ofheaters 3 and 5, cathodes 7 and 9, control grids 11 and i3, and one ormore apertured accelerating electrodes 15 and 17 shown here forconvenience as mechanically internally connected to the envelope andhence electrically at the same potential and at the potential of theenvelope. The electron guns are arranged to project two electron beamswith their average direction parallel to the axis of the electron tube.A constant magnetic field of strength where m and e are the electronicmass and charge, re spectively, and m is the angular frequency of theR.F. voltage used to excite the electron tube, as explained in greaterdetail below, is caused to extend along the axis of the device, withinthe envelope. This magnetic field may be produced by any suitable means,as, for example,

7 now be explained by reference to Figs. 1-3.

a maximum value.

by an electro magnet, or a permanent magnet external to the tube andmaking use of the pole pieces P-P- of Fig. 1.

Within the envelope of the tube, in theembodiment of Fig. l, are threesets of pole faces 19, 2 1 and "2 3. In each pair, such as 19, the twopole faces are spaced on opposite sides of the tube axis. Although thepole faces are shown as flat plates, supported by extensions 24, 25,27of the envelope, the pole faces may be arcuate in form and may besupported in any other suitable manner, such as from partitions locatedat the ends thereof, a method of support which is illustrated in Fig. 4and discussed in connection .with that figure. In Figs. 1-3 each of theelectron beams passes through two of the regions of the tube containingthe pairs of pole faces. In Fig. 1 the pairs of pole faces are sosupported, and the discharge device is so divided into three regions, bythe accelerating electrodes 15 and 17 which also serve as partitions andby two other partitions 29 and 31 perpendicular to theaxis of the tube,that three separate resonant cavities or cavity resonators are formed.This construction is shown as an example only. Alternatively, electricalconnection'may be made between the pole faces and external circuits, sothat resonant circuits are formed which are situated partly within andpartly exterior to the envelope of the tube. In the form illustrated inFig. 1 the entire resonant circuit is in each case contained within theenvelope with coupling means such as loops 33, 35 and 37 f suitable formconnected to external transmission lines 39, 41 and 43 so thatenergy atradio frequency may be introduced into the resonant cavities or removedfrom them.

In the operation of the embodiment of the invention shown in Figs. 1-3the envelope 1 is connected to a source of direct current potential,such as the battery 45, and

the cathodes 7 and 9 are connected to the same source of potential, in amanner such that the envelope is maintained at a potential highlypositive with respect to the potentials of the cathodes. The cathodesmay beat the same or at somewhat different potentials. The intensitiesof the two election beams are adjusted by varying the potentials of thecontrol grids, which potentials are preferably negative with respect tothe potentials of the corresponding cathodes. The two electron beams arecollected at the anodes 47 and 49 which are suitably cooled and maybemaintained individually at potentials which are the same or differentfrom the potential of the envelope 1.

The operation of one embodiment of the invention will A source of radiofrequency, designated as input No. 1 is coupled through line 39 and loop33 to the above-described resonant cavity formed by elements 1, '19,2.4, 15 and 29. Input No. 1, of angular frequency w =H@/m produces aperiodically varying voltage between pole faces 19 ith the electricfield directed perpendicularly to these pole faces. As is described in.detail in Patent No. 2,542,797, the electrons in the bearrr moving tothe right in Fig. 1 gain energy from the R.F. field arising from inputNo. 1 and execute circles of increasing diameter as they pass betweenpole faces 19. One possible conical envelope 51 of their trajectories isshown by dotted lines in Fig. 1. i a directrix of the cone shown so thateither dotted line of the cone '51 may be considered to be the positionsoccupied by the electrons at one instant of time. The dotted linebetween grid 11 and the left-hand edge of pole faces 19, in Fig. 1,represents, for convenience, an infinitely thin beam, although the beammay be caused, by suitable means, to have a diameter of almost anydesired value. 'When the beam is in the plane of the figure, the RF.voltage between the pole faces will have If the force on the electron isdirected out of the plane of the figure and toward the ob: server, andis at its maximum value, theindividpal elecr At any instant allelectrons lie along q A We trons lie in the plane of the figure and aremoving toward the observer. Thus the position of the directrix beam atany instant. is uniquely determined by the phase of the R.F. voltagebetween the pole faces of the resonant cavity Furthermore the conedirectrix beam becomes an element of a cylinder after the electronsleave the pole faces 19. As long as the electrons are in a resi nin itemR-F- r e e d the ont n to revolve around the tube axis at the sameangular frequency, as they move, individually, in a spiral path down thetube yvith the pitch of thespiral determined only by the axial velocityimparted by the DC. axial field. Thus information as to the phase of theR.F. voltage between the pole faces is retained .by the electrons afterthey leave the pole faces, for, as an exexample, at any instant when allelectrons are in the plane of the figure "and moving toward theobserver, the force on the electrons (oppositely directed to the R.F.field) within the pole faces has again assumed a maxivalue and directedperpendicularly to this plane and in a direction toward the observer. I

In the'same manner, the other electron beam, arising at the electron gunformed by elements 5, 9 and 17, but proceeding toward the left in Fig.1, retains information concerning the phase of the R.F. voltage betweenthe pole faces 23 which, together with elements 1, 17, 31 and 2 5 form aresonant cavity coupled to input No. .2 by loop 37 and line 43. Thedirection of rotation. of the trace of each beam on any section, such asFig. 3, of Fig. 1 is determined by the direction of the constant axialmagnetic field. This direction is independent of the direction of axialmotion of the spiralling electrons. Therefore, the directions ofrotation of the two cone directrix. beams, theenvelopes of which areshown by 51 and '53, are the same, although their instantaneouspositions in a plane perpendicular to Fig. 1 are determined only by thephases of the RF. voltages between the pairs of pole faces through whichthey have separately passed; Each of the 'two cone-directrix beams 51and 53 is generated independently of the other beam, by the separateelectron gun and separate R.F. field means, combined with the commonmagnetic field. Beam 51 retains information concerning the phase ofthe.R.F. voltage between plates 19; beam 53 retains informationconcerning the phase of the R.F. between plates 2$Q These phases may bequite different. It is of course well known that the phases of the RF.voltages b etWee n the pole faces differ from the phases at the sourcesindicated by input No. 1' and input No. 2, but the phase differencesbetween the inputs and the corresponding pole faces are substantiallyconstant, so that "any change in phase at input No. 1 or input No. 2 isaccompanied by substantially the same change in phase atthecorresponding pole faces. The electrons,

' .as high as from one to one times the radio frequency is substantiallycompletely. indicated by the new angular position assumed by thecone-directrix or cylinder element electron beam.

The invention has now been described up'to the point of showing how theelectron beams, leaving the resonant cavitiesshewn connected to inputNo. l and input No. 2 of Fig. 1, have instantaneous positions indicativeof the phases, atthesameinstants, of the R.F. voltages between p e faces.9 an .3,- It w l HOW be s wn hatths device can preducean output in aload which output indicates by its magnitudethe relative phases or theR.-F. voltages between poles faces 1-9 and 230. and, after a correctionfor the constant phase differences mentioned above, the relative phasesof inputs No. 1 and No. 2. The central cavity of the device asillustrated in Fig. 1 is coupled by the loop 35 and line 41 to theoutput load. An additional shunt load 55 is shown in parallel with theoutput load. The total loading presented by the shunt load and theoutput load are adjusted to the desired value as described in greaterdetail below, although the output load alone may alternatively bedesigned to have the desired characteristics.

As explained in detail in Cuccia Patent No. 2,542,797, when the beam 51,for example, enters the central resonant cavity, a voltage is induced inthe pole faces 21 in a phase exactly opposite to the phase of thevoltage between pole faces 19. The radius of revolution of the electronsis progressively reduced as they pass between pole faces 21, so that thecone directrix beam is a directrix of a cone converging as shown by theenvelope 57. The radius of revolution of the electrons is smaller whenthey leave the pole faces 21 than upon their entrance. Since the totalspiral energy per electron varies as the square of the radius ofrevolution, energy has been lost. This spiral energy has beentransformed to the resonant circuit and, neglecting circuit losses, tothe output load. The degree of convergence of the envelope between thepole faces depends upon the resistive portion of the total output load,here the shunt load 55 plus the output load as illustrated. When theresistance R of the output load, expressed as the transformed resistancepresented across the pole faces 21, has the specific value defined by:

V d 2 hir) (2) where V is beam accelerating voltage in volts, I is theelectron beam current in amperes, L is the length of the pole faces andd is the distance between them, both in centimeters, the beam willconverge so that the radius of revolution of the electrons is Zero asthey leave the region between the poles faces 21. Equation 2 correspondsto Equation 15 of Cuccia Patent No. 2,542,797. If R has a value greaterthan R the beam will converge before it has passed completely betweenthe pole faces, beyond which point of convergence the electrons willrotate with a radius of revolution increasing again so that the beam isthe directrix of a cone with its apex pointed to the left in Fig. 1. IfR has a value less than R the beam will not be completely converged whenit leaves the region between the pole faces.

In accordance with the invention both beams 51 and 52 absorb energy asthey pass between pole faces 19 and 23, respectively, and both beamsinduce voltages in the output pole faces 21. Only one voltage can existbetween pole faces 21, which voltage is the vectorial sum of thevoltages induced by the two beams.

As an example, it is assumed that the two beam currents are adjusted toequality and that the amplitude of the radio frequency voltage betweenpoles faces 19 is equal to the amplitude of that between pole faces 23,although neither condition is required for the effective operation ofthe invention. It is further assumed as an example that R equals R givenby Equation 2 where I is the sum of the currents in the two beams. Whenthe radio frequency voltages between the pairs of pole faces 19 and 23are exactly in phase, the beams entering the pole faces 21 are rotatingin the same direction and they are in the same spatial phase, i.e., ifat one instant beam 51 is in the plane of the section of Fig. 1 andmoving toward the observer, the other beam is also in the plane of Fig.1 and moving toward the observer. The voltages induced separately bybeams 51 and 53 in pole faces 21 are in exactly the same phase so thattheir vectorial sum is in the same phase as either voltage consideredseparately. Since Equation 2 is satisfied, both beams converge to zeroradius of revolution just as they leave the pole faces 21. As will bemade clear in greater detail below, the preferred value of R should beequal to or less than R given by Equation 2 where I is the sum of thebeam currents. For R somewhat less than R given by Equation 2, the beamswill converge equally, but not quite to zero radius of revolution, asshown in Fig. 1.

The example given above, in which the two beams were in the same spatialphase upon entering the pole faces 21, resulted in a total inducedvoltage, between pole faces 21, equal to the sum of the separatelyinduced voltages. Each electron beam gave up an amount of powerproportional to the square of the difference between the electron radiusof revolution upon entering and upon leaving the pole faces 21. Thevoltage developed across the output load was equal to the square root ofthe quantity equal to the sum of the powers lost by both beams dividedby the resistance of 55 and the output load in parallel.

Let it be assumed that the beam currents remain unchanged but that thephase of the radio frequency voltage across pole faces 19, for example,is altered by 180 electrical degrees. The beams now enter the outputpole faces 180 degrees out of phase spatially. Since the beam currentsare equal, as assumed, the two beams tend to induce equal voltages inpole faces 21 but these voltages are 180 out of phase so that the netinduced voltage is zero, and the beams are not collapsed at all. Nopower is given up to the resonant cavity and no voltage appears acrossthe output load.

As a third example, it is assumed that the radio frequency voltagesacross the pole faces 19 and 23 are electrically out of phase. The twobeams enter the pole faces 21 with their instantaneous radii ofrevolution at 90 in space. The voltages induced in pole faces 21 are 90out of phase in time so that the vectors representing the two voltagesmust be drawn at 90 to each other The sum vector lies, in magnitude,between zero and the maximum value reaches when the radio frequencyvoltages were in phase between the pole faces 19 and 23.

Thus it is seen that the device shown in Fig. 1 produces an RF. voltageacross the load which is indicative of the relative phase of the RF.voltages between pole faces 19 and 23, and hence, indicative of therelative phase of the radio frequency voltages of input No. 1 and inputNo. 2, although due to the line-lengths between the inputs and theresonant cavities, and between the central resonant cavity and theoutput, the voltage across the output load may not be a maximum when thetwo inputs are in phase. This last is not of fundamental importance,since account can be taken of the fixed line lengths. For example, thetwo inputs can each be situated electrically an integral number ofwavelengths at angular frequency (0 from the electrical planes of polefaces 19 and 23, respectively, and the output load can be electricallysituated an integral number of wavelengths at angular frequency w fromthe electrical plane of pole faces 21. The radio frequency "oltageacross the output load is then a maximum when the radio frequencyvoltages of inputs No. 1 and No. 2 are in phase, and decreases as theseradio frequency voltages become out of phase.

Within the scope of the invention, the radio frequency voltage acrossthe output load may be used directly for control purposes, for example,as a radio frequency voltage of an amplitude indicating the relativephase of the radio frequency voltages of inputs No. 1 and No. 2.Alternatively, the voltage across the output load may be rectified andfiltered so that a DC. voltage is obtained with a magnitude indicativeof the relative phase of the radio frequency voltages across inputs No.1 and No. 2. In this case the DC. voltage will show whether the radiofrequency voltages of the inputs are in phase, out of phase, or at someintermediate phase. In the latter case, however, the DC. voltage willnot show which input voltage is ahead in time phase. In many cases thisinformation is entirely unnecessary, as will be made clear by a laterexample.

It was stated above that in the preferred form of the invention thevalue of the total load resistance is that givenby Equation 2, or isless than this value. Assume, as anexample, that the total loadresistance R is greater han that given by 2. When the two beams enteringthe pole faces 21 are in phase, spatially, each will be completelyconverged and will begin to diverge again before it leaves the polefaces, Power will be given up, however, and a voltage will appear acrossthe output load. Now suppose that the input voltages alter their phaseso that the beams'are somewhat out of phase spatially as they enter theregion between pole faces 21. The total radio frequency voltage inducedin pole faces 21 will be reduced as the two vectors assume an angle toeach other. The convergence of the beams will be decreased, so that fora particular phase they will be completely converged just as they leavethe pole faces 21. The power remaining in the beams is reduced, so thatthe power going to the output load is increased. The voltage across theoutput load rises, rather than falls as in the above example, as theinput radio frequency voltages go out of phase. Since the voltage acrossthe output load falls again for still greater phase differences betweenthe input.

voltages, there will be a single voltage across the output load for twovalues of phase difference between the input voltages. While in manycases this will not degrade the performance of the invention, thepossible existence of such a behavior should be taken into account.

Figure 4 is a longitudinal sectional view of another embodiment of theinvention and Fig. 5 is a transverse sectional view taken on line 55 ofFig. 4. In this case two input resonant cavities, 5t; and 59, are placedside by side within the envelope 1, and two electron guns at and63,.also placed'side by side, cause electron beams to pass alongparallel paths in the same direction. Another of the possible forms ofconstruction of the resonant cavities, equally applicable to Fig. 1, hasbeen shown in Figs. 4

a and 5. Arcuate pole faces 65 and 67 are supported at "patentapplication of C. L. Cuccia, Serial No. 216,320,

filed March 19, 1951, now Patent No. 2,806,172, the beam at any instantis not the directrix of a cone, but all electrons lie at any instant ina plane parallel to the axis of the resonant cavity and passing throughthis axis. The

path of the beam is not'a straight line, but a curve as shown at 75.

Except as described, and the mode of operation of the embodiment ofFigs. 4 and 5 is similar to that of Figs. 1-3. The parts serving thesame functions as Fig. 1 have been given the same numbers. The radiofrequency voltage across the output load is again indicative of therelative phase of the radio frequency voltages of the two inputs. i

An example will now be given of the use of the invention'for the controlof radio frequency oscillators. Let it be assumed that a magnetronoscillator is to be'synchronized with a crystal controlled oscillator bythe proce dure known as phase locking, so that under equilibriumconditions the frequencies of the two oscillators are identical andthereis a fixed phase relation between the two oscillators unless aneffort is made to perturb the frequency of one of the oscillators, as byplate modulating the magnetron. The embodiments of either Fig. 1 or Fig.4 would serve for this purpose. Fig. 1 will be chosen forpurposes ofillustration.

i Let input No. 1 represent the magnetron and input No. 2 represent thecrystal controlled reference oscillator. It

is assumed that the magnetron is equipped with an electronic mechanismfor the control of its frequency, such as the frequency control electronguns described in Dona-1 et al. Patent No. 2,602,156, assigned to RadioCorporation of America. The control grids of these frequency controlguns serve as the'output load, with the'shu'nt load serving fortheadjustrnent of the total load resistance to the desired value asdescribed earlier. When the radio frequency voltages from the magnetronand the control oscillator are in phase at the pole faces 19 and 23respectively, the radio frequency voltage across the output load, afterrectification and filtering, gives a maximum voltage at the grids of themagnetron control guns. If the phase of the magnetron alters, thevoltage at the grids of the control gun decreases. If the voltages fromthe magnetron and from the crystal controlled oscillator are 180 out ofphase at the respective pole faces, the voltage at the grids of thecontrol guns will be zero. It is assumed that by Well-known means anindependent DC. bias is applied to the grids of the control guns andthat when the magnetron phase rnoves either ahead or behind the phaseofthe. crystal controlled oscillator by 90 (the phase of the voltage atthe pole faces is meanthere and in the following), producing in eithercase the same reduced voltage at the grids of the control guns, the D.C.bias is so adjusted that the frequency of the uncontrolled magnetron isequal to that of the crysal-controlled oscillator. It is furtherassumed, as an example only, that the addition .of more signal from thephase discriminator of Fig. 1, to this bias, causes the beam current ofthe frequency control guns to increase and causes the frequency of themagnetron to tend to decrease. Such a tendency to decrease would retardthe phase of the magnetron with respect to the crystal-controlledoscillator.

- The condition for stable phase difference between the two oscillatorswill now be examined. Suppose the magnetron is initially 90 in phaseahead of the crystal-controlled oscillator. The vector diagram is shownin Fig. 6.

The magnetron voltage, '77, leads the crystal-controlled oscillatorvoltage, 79, by 90 at the pole faces 19 and 23, respectively. Theresultant output voltage across the load has the magnitude shown at 81.This voltage, rectified, addsto the bias of the frequency-control guns.Suppose the magnetron voltage 77 is caused, by plate modulation, forexample, to move ahead in phase to a newposition 83. The resultantvoltage at the control grids from the phase discriminator is reduced asshown at 85. The total voltage at'the control grids is reduced and thedecreased beam current of the frequency-control guns causes themagnetron frequency to tend to increase. This advances the phase of themagnetron still further and no phase stability has been found. However,the

' magnetron phase advances until it is 90 behind the phase of thecrystal-controlled oscillaton'as shown at 87. Here the two radiofrequency voltages add to produce a resultant rectified voltage 89' atthe grids of the frequency control guns. If now the magnetron tries toadvance in phase,

the voltage at the grids is increased, the frequency-control gun beamcurrent is increased, and the magnetron frequency tends to decrease. Anyphase advance of the magnetron beyond 87 results in a correcting signalwhich retards the phase again. Correspondingly, any retardation in phase87, gives a signal tending to advance the phase. When the magnetron is90 behind the crystalcontrolle d oscillator, stable phase locking isobtained. Of course, if increasing positive signal on the grids of thefrequency-control guns were made to raise the magnetron frequency,rather than to' lower it, stable phase locking would be found with themagnetron ahead of the crystal-controlledoscillator.

From the above it is seen that either of the embodiments of theinvention so far described can be used to phase lock two oscillatorstogether; If one of these oscillators is assumed to have .a stablefrequency, as in the above case, the second oscillator is made to have astable frequency.

From the descriptions taken in connection with Figs. 1-6, it is evidentthat the invention can be used, for example, to control very high poweroscillators. Two of the devices shown in Fig. 1 or Fig. 4 could be used,as another example, to control the frequency and phase of two magnetronswith reference to a single crystal-controlled oscillator. By modulatingthe grid voltages of the frequency-control guns in the magnetrons, thephase of one tube can be caused to advance and the phase of the other toretard. If the outputs of the two magnetrons are properly combined in aload, such as an antenna, an amplitude modulation system results. Incombining the powers in an antenna, however, it is difficult to preventthe reaction of one oscillator upon the other. Various means,'such asradio frequency bridges, have been used for this purpose. With thisdevice, when the two voltages are in phase at the load, the power notdesired in the antenna is dissipated in a dummy load.

As a further embodiment of the invention, the combination of the powerfrom two phase-controlled oscillators is accomplished by an electrontube similar in principle to that of Figs. 1-5. The two phase-controlledmagnetrons, for example, serve as inputs No. 1 and No. 2 of Fig. 1.Their power is absorbed by the beams 51 and 53 and delivered to theoutput load. When the phases of the two inputs are the same, at polefaces 19 and 23, respectively, all of the power output of bothoscillators reaches the output load, provided that the resistance R ofthe output load (the shunt load is eliminated in this embodiment)satisfies Equation 2 where I is the sum of the two beam currents. Forbest operation, the two beam currents of Fig. 1 should be equal. Whenthe controlled phase of input No. 1, for example, is advanced, and thatof input No. 2 is retarded, the power in the output load is decreased.If the phases of inputs No. 1 and No. 2 are made 180 different, at thepole faces, the power in the output load falls to Zero. The power notreaching the output load is dissipated on the water-cooled collectorelectrodes 47 and 49. Due to suitable electromagnetic decoupling betweenthe central output cavity and the two input cavities, or circuits, oneoscillator cannot react upon the other. If one oscillator is advancedwhile the other is retarded by the same amount, and if the beam currentsare the same, as proposed, amplitude modulation without phase modulationis produced by this embodiment of the invention.

Still another embodiment of the invention is shown partly schematicallyin Fig. 7. As in Figures 1 and 4, two electron guns 91 and 93, within anenvelope 95, project beams 07 and 99 parallel to an axial magnetic fieldH and between pairs of pole faces 101 and 103. These pole faces may formportions of resonant cavities or may be connected to external resonantcircuits. The beams enter the space between a pair of pole faces 105connected by suitable means to the output load. The envelope 95 and thecollector electrodes 107 and 109 are held at potentials, which may bethe same, high with respect to the potentials, which may be the same,high with respect to the potentials of the cathodes, by means of asource of potential such as the battery 111. The control grids of theelectron guns are suitably biased by means of sources of potential suchas the batteries 113 and 115.

The operation of the embodiment of the invention shown in Fig. 7 will beunderstood from the following description. A radio frequency generatoris suitably con-' nected to the pole faces 101 in such a manner that aradio-frequency field is produced between said pole faces. The electronsof the beam 97 gain spiral energy from this field so that a portion ofthe power output of the radio frequency generator is absorbed by thiselectron beam in the manner described in connection with Fig. 1. Thesame radio frequency generator is connected to a phase shifter which isin turn suitably connected to the second pair of pole faces 103 so thatpower from the radio-frequency generator is absorbed by the electronbeam 99. The circuit and the beam currents are so adjusted thatsubstantially equal portions of the power from the radio-frequencygenerator are absorbed by the beams. The phase shifter is a device knownin the art, which might consist of variable reactances suitablyconnected to lengths of transmission lines, the whole having theproperty of shifting the phase of the radio-frequency voltage, at theoutput of the device, with respect to the phase of the radio-frequencyvoltage at the input of the device. The degree of phase shift iscontrolled by a modulator. By means of the modulated phase shifter thephase of the radio frequency voltage appearing between pole faces 103may be shifted with respect to the phase of the radiofrequency voltageappearing between pole faces 101. As

explained by the earlier description taken in connection.

with Fig. 1, the revolving cone-directrix beam formed between the pairsof input pole faces will enter the region between the output pole faces105 with relative spatial phases of revolution which differ from eachother by the electrical phase dilference of the radio frequency voltagesimpressed between pole faces 101 and 103. When the spatial phases ofrevolution of the beams are equal, maximum power will be transferred tothe output load, which should have a magnitude given by Equation 2 whenI is the sum of the two beam currents. When the two beams are in spatialphase opposition, no power is transferred to the output load, but all ofthe power in the beams is dissipated in the suitably cooled collectors107 and 109. For intermediate phases, a portion of the power from theradio frequency generator reaches the output load, the remainder goingto the collecting electrodes.

It will now be seen that the invention accomplishes amplitude modulationin response to a signal arising from the modulator. Alternatively twophase shifters might be connected between the radio-frequency generatorand the respective pairs of pole faces, so that a single modulatoracting upon the two phase shifters would advance the spatial phase ofone electron beam while retarding the spatial phase of the second beam.Amplitude modulation would be accomplished, with the difference that thesymmetrical operation would maintain constant the phase of the radiofrequency voltage across the output load.

Still another embodiment of the invention is shown in Fig. 8. Thisembodiment performs the useful function of a balanced modulator.

A balanced modulator is an electronic system widely used forapplications where carrier suppression in a modulation system isdesired. In many systems of radio-telephone transmission, for example,the carrier is suppressed at the transmitter by using a balancedmodulator; only the side bands are transmitted which, upon arriving atthe receiver, are recombined with a locally produced carrier and thendemodulated in customary fashion. Such a system is useful for insuringprivacy during the transmission.

Also in many types of frequency-modulated transmitters, thefrequency-modulated wave is produced by beginning with an amplitudemodulated wave which is then applied to a balanced modulator whichremoves the carrier. The resulting side bands are then shifted to aproper phase and recombined with a carrier so that the output is a phaseor a frequency-modulated wave.

The embodiment shown in Fig. 8 is also an improvement over conventionalbalanced modulator circuits since in addition to having the capabilityof functioning as a balanced modulator at frequencies much higher thanthose at which standard circuits will perform efliciently, it is alsovery versatile in that it can be used to suppress the carrier in eitherF.M. or A.M. transmisssion.

Consider first one method of operation of the embodiment in Fig. 8 forthe purpose of suppressing the carrier during amplitude-modulationtransmission, utilizing one set of phase conditions which yield thedesired result. In Fig. 8 the same numerals as in Fig. 7 are used toindicate "ll elements'performing the same function as in the cmbodi-'-'ment of Fig. 7. i 3

Here let the adjustment of a phaseeinverter, between a radio-frequencysignal generator and the pole faces 1%, be such that a phase-shiftedsignal -E cos w t appears across pole faces 103 while a signal E cos w tappears across pole faces 101, where is the angular frequency of thesignal and is also the cyclotron angular frequency. Then let amodulating signal E sin ta l from a modulator be applied to thecoupling-beam gun 91 and let the. phase inverter in line to couplingbeam gun 93 be adjusted so that the signal E M cos w t be applied tothis gun, where a is the angular frequency of the modulating signal.

Between the output pole faces 1%, the transverse electric field will be180 out of phase with respect to the signal. E cos w t being to appliedpole faces 1M and 1&3; therefore the current which will appear in theload circuit from output pole faces ltlS will be o=iol+i where 1' is theelectron current due to the coupling beam 97 and 1' is that due to thebeam 99.

The currents i and i will be of the forms, where M is the modulationfactor:

The removal of the carrier or any side frequency from a frequencymodulated wave can be accomplished in an equally simple fashion by theembodiment shown schebe applied to the pole faces 103 Where Aw is themaximum frequency deviation and m and w are the angular frequenciesofthe carrier wave and of the modulating wave, respectively. Then let aconstant amplitude signal (assuming that the carrier is to besuppressed) be impressed across the pole faces 101. The amplitudes V ofthe beams are maintained constant.

it is evident that a signal of frequency to will not appear in theoutput load, thereby resulting in carrier suppression.

' Note that should the signal frequency, and the other source is asource of constant p 12 be impressed across pole faces 101, the signalat frequency o +nw will be suppressed inthe output.

' What is claimed is:'

1. An electron'beam tube comprising: first and second means forindependently generating two radio frequency beams of electronsspiralling about two parallel axes at ference between said sources.

2. An electron beam tube as in claim'l, wherein said first-named meanscomprises two electron guns arranged to project two electron beams alongsaid two parallel axes, separate means responsive to two differentsignals for establishing a radio frequency electric field transverse toeach of said two beams in a region traversed by'that beam only, thephase of each electric field being determined by the phase of therespective signal producing said field, and means for establishing aconstant magnetic field along both ofsaid beams parallel to said axes.

3'. The combination of the electron beam tube of claim 9 with two radiofrequency sources having the same.

angular frequency substantially equal to where H the strength of saidmagneticfield, and e and m are the charge and mass, respectively, of anelec tron, but having any phases, coupled respectively to said separatemeans.

4. The combination of claim 3, wherein said two sources are independentradio frequency generators.

5. The combination of claim 3, wherein one of said electric fieldestablishing means is coupled directly to a radio frequency generator ofsaid frequency, and the other electric field establishing means iscoupled through a phase-shifting means to the same generator.

6. The combination of claim 5, further including a modulator coupled tosaid phase shifting means.

7. The combination of claim.5, wherein said phaseshifting means is aphasednverter, and further including means for applying a modulatingsignal to said two beams in opposite phase. a

8. The combination of claim 3, wherein one of said sources is a voltagesource of constant amplitude and index frequency-modulated voltage.

9. An electron beam tube including first, second and third electrodestructures, each adapted to be energized to establish a radio frequencyelectric field transverse to a. predetermined axis of the tube, meansfor projecting a first beam of electrons parallel to said axis andthrough the fields of said first and second electrode structures only,in that order, means for projecting a second beam of electrons parallelto said axis and through the fields of said third and second electrodestructures only, in that order, and means for establishing a constantmagnetic field through all of said structures parallel to said axis,each of said first and third electrode structures having radio frequencyinput coupling means adapted to be coupled to a separate radio frequencysource, said second electrode structure having radio frequency outputcoupling means adapted to be coupled to an output load. 7 10. Anelectron beam tube as in claim 9, wherein said first, second and thirdelectrode structures are aligned with each other along said axis in theorder named.

11. An electron'beam tube as in claim 9, wherein said first and thirdelectrode structures are juxtaposed on oppo- Sides at sa d xi an a smn at des tae 14 Donal Aug. 21, 1951 Donal et a1 July 1, 1952 Mesner Sept.30, 1952 Cuccia May 12, 1953 Cuccia Sept. 10, 1957 OTHER REFERENCESProceedings of the Institute of Electrical Engineers, vol. 100, No. IV,5, October 1953, pages 16 to 24.

